Apparatus for the application of fluoropolymer coating to internally threaded fasteners

ABSTRACT

An apparatus for the application of a fluoropolymer coating to the threads of an internally threaded fastener. The fastener has a body and a threaded bore extending to opposing ends of the body to define opposing first and second openings in the fastener. A conveyor moves the fastener along a path of travel with its threaded bore in a predetermined orientation. An obstruction member closes, the first opening, while a nozzle directs an air stream carrying entrained fluoropolymer powder through the second opening and into the threaded bore. The nozzle is stationary and is located at an axially displaced position relative to the second opening of the fastener and immediately adjacent the conveyor. A heating station heats the fluoropolymer powder to its melting temperature causing it to melt and fuse into a generally continuous film covering the fastener&#39;s threads.

This application is a divisional of prior application Ser. No.10/428,162, filed May 1, 2003 now U.S. Pat. No. 6,972,137.

BACKGROUND OF THE INVENTION

The present invention relates generally to coatings for threadedfasteners. More particularly, the invention relates to a process andapparatus for the application of fluoropolymer coatings onto the threadsof internally threaded fasteners.

It is now well known that fluoropolymer coatings may be advantageouslyemployed to mask or protect the threaded portions of fasteners fromvarious contaminants, such as paint primer, anticorrosion materials,weld spatter and the like. A preferred technology for the application ofthese coatings uses a fluoropolymer which is applied in dry powder formand is heated to form a thin continuous coating over the fastenerthreads. Typically, the powdered fluoropolymer is entrained in an airstream which is directed onto the threads of the fastener by means ofspecially designed nozzles. Examples of this preferred technology areillustrated in U.S. Pat. Nos. 4,835,819, 5,221,170, 6,156,392 and6,395,346, whose disclosers are incorporated herein by reference.

One problem with the known prior art processes occur when coatinginternally threaded fasteners. Because of the need for generally uniformand continuous coatings, it has heretofore been the practice to insertthe nozzle within the threaded bore of the fastener during powderapplication. This practice requires a reciprocating nozzle design whichcan be mechanically complex and costly. It also results in generallylower production rates as compared with other powdered coatingtechniques with a stationary nozzle design.

It would be desirable, therefore, to employ a stationary nozzle designfor the application of fluoropolymer coatings to internally threadedfasteners, while still maintaining a high degree of coating uniformityand continuity over the fastener threads.

SUMMARY OF THE INVENTION

In accordance with the present invention, it has been found that uniformand continuous fluoropolymer coatings may be obtained across the threadsof internally threaded fasteners, using a stationary nozzle positionedadjacent one end of the fastener. Surprisingly, the desired coating isachieved, in part, by blocking or closing the opposite end of thefastener while the powder is applied.

In one aspect of the invention, a process and apparatus are provided forthe application of a fluoropolymer coating to the threads of aninternally threaded fastener. The fastener has a body and a threadedbore extending to opposing ends of the body to define opposing first andsecond openings in the fastener. The fastener is moved on a conveyoralong a path of travel with its threaded bore in a predeterminedorientation. As the fastener moves along its path of travel, the firstopening is closed by means of an obstructing member, while an air streamcarrying entrained fluoropolymer powder is directed from a nozzlethrough the second opening and into the threaded bore. The nozzle isstationary and is located at an axially displaced position relative tothe second opening of the fastener and immediately adjacent theconveyor. Preferably, the nozzle includes a diffuser which directs theair stream and entrained fluoropolymer powder into the fastener bore ina diverging pattern. After the fluoropolymer powder is deposited ontothe threads of the fastener, the conveyor moves the fastener through aheating station where the fluoropolymer powder is raised to its meltingtemperature causing it to melt and fuse into a generally continuous filmcovering the fastener's threads.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are characteristic of the present invention areset forth in the appended claims. However, the invention's preferredembodiments, together with further objects and attendant advantages,will be best understood by reference to the following detaileddescription taken in connection with the accompanying drawings in which:

FIG. 1 is a schematic illustration of an exemplary embodiment, showingthe overall arrangement of a process and apparatus for application offluoropolymer onto threaded fasteners in which the present inventionfinds particular utility;

FIG. 2 is a perspective view illustrating details of construction forone preferred embodiment of the present invention;

FIG. 3 is a side elevational view showing further structural details fora powdered fluoropolymer application station employed in one preferredembodiment; and

FIG. 4 is another side elevational view in partial cross section andillustrating still further structural details for the applicationstation shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The process and apparatus of the present invention may be advantageouslyused with any variety of internally threaded fasteners. Such fastenersinclude a fastener body having a threaded bore extending to the opposingends of the body, thereby defining first and second openings at each endof the fastener body. The fasteners may be supplied as individual items,in bulk, or strung together on a wire and supplied on a reel.

FIG. 1 illustrates a process for applying fluoropolymer to the threadsof internally threaded fasteners where the fasteners are joined by awire carrier and supplied from a feed reel 10. The fasteners areconveyed from the feed reel through a washing station 12, a powderapplication station 14, a cleaning station 16, a heating station 18 andan anticorrosion station 20, and finally to a take up reel 22.

Any of a variety of fastener conveyors well known to those of skill inthe art can be used to move the fasteners along a path of travel throughthe various processing stations. Where the fasteners are supplied loosein bulk, conveyors as shown in U.S. Pat. Nos. Re. 33,766, 5,792,512, andU.S. Pat. No. 6,296,573 B1 may be used.

When the fasteners are strung on a carrier wire, the conveyor may takethe form of a track 24, as shown in FIG. 2, having parallel channelrails 26 and 28, with the fasteners being moved along the desired pathof travel by one or more drive wheels 30.

At the powder application station, the fastener's first opening (asshown in the drawings, the “first” opening is at the top of the fastenerbody) is closed by an appropriate obstructing member which may take theform of a plate or belt or, as illustrated, a rotating wheel. Thus, inthe preferred embodiment, wheel 30 serves both to move the fastenersalong the track 24 and to close the upper opening of each fastener as itpasses through the powder application station. Wheel 30 may be made ofrubber-neoprene or polyurethane with a durometer range of Shore A 30 to70. Alternately, the wheel should be soft enough in construction to forma seal so as to close the upper opening of each fastener.

While the first or upper opening of the fastener is closed by wheel 30,an air stream carrying entrained fluoropolymer powder is directed fromnozzle 40 through the second or lower opening and into the threaded boreof the fastener.

The nozzle 40 is stationary and is positioned immediately adjacent thefasteners' path of travel. The nozzle 40 includes a pressurized airinlet 42, a powder inlet 44 and an outlet port 46 which directs the airstream and entrained fluoropolymer powder into the fastener's threadedbore. Preferably, the nozzle also includes a diffuser or deflector 48axially mounted within outlet port 46 which generates a diverging airstream carrying the fluoropolymer powder into the fastener bore. Theangle of the diffuser or deflector is preferably 60 degrees from theaxis of the outlet port, however, a range between 30 to 80 degrees maybe used as well. An annular vacuum port 50 may also be situated adjacentoutlet port 46 to collect fluoropolymer powder which is not deposited onthe threads of the fastener. The vacuum level may be adjusted to controlthe uniformity of the powder coating deposited onto the threads of thefastener. For larger sized fasteners, it has been found that more vacuummay need to be used to maintain a uniform coating. The amount of coatingapplied to the fastener may be determined by the volume of powderapplied and the number of powder applications.

The wheel 30 may pick up fluoropolymer powder on its outercircumferential surface, and this powder may be removed by a vacuumcleaner 52 whose port 54 is positioned adjacent the wheelscircumference.

Any fluoropolymer powder deposited on the lower surface of the fastenermay be removed at the cleaning station 16. In the preferred embodimentthis cleaning is accomplished using a belt 56 with bristles or a Velcrosurface 58. Once again the powder build up on the cleaning belt 56 maybe removed via vacuum cleaner 60.

The fluoropolymer powder collected from vacuum devices 50, 52 and 60 maybe recirculated to the powder supply which feeds nozzle 40.

After the fluoropolymer powder is deposited on the fastener's threads,the fastener moves through a heating station, such as induction heaterelements 62 and 64 to raise the fluoropolymer to its melting temperaturewhereby the individual powder particles melt and fuse into a generallyuniform and continuous film coating. A preferred particle size is from20 microns to 35 microns.

As those of skill in the art will appreciate, the process and apparatusof the present invention is mechanically simple, requiring only verybasic mechanical components. Because there is no need to reciprocate thepowder application nozzle into and out of the fastener bore, thefasteners may move continuously and production rates may be enhanced.

1. An apparatus for the application of a fluoropolymer coating to thethreads of an internally threaded fastener, said fastener having a bodyand a threaded bore extending through the body to opposing ends of thebody to thereby define first and second opposing openings in thefastener, said apparatus comprising: a conveyor to move the fasteneralong a path of travel with the fastener's threaded bore in apredetermined orientation; an obstruction member positioned adjacent thefastener path of travel and having a surface which engages an end of thefastener body and closes the first opening of the fastener; a stationarynozzle positioned adjacent the fastener path of travel and axiallydisplaced from the second opening of the fastener, said nozzle having apressurized air input, a fluoropolymer powder input and a outlet port tothereby direct an air stream carrying entrained fluoropolymer powderthrough the second opening and into the bore of the fastener while thefirst opening is closed by the obstruction member, thereby forming afluoropolymer powder coating on the threads of the fastener; a heatingelement positioned along the fastener path of travel to heat thefluoropolymer powder to its melting point to form a fluoropolymer filmon the threads of the fastener.
 2. The apparatus of claim 1 wherein theobstruction member is a rotating wheel having an outer surface whichabuts the end of the fastener and thereby closes the first opening ofthe fastener.
 3. The apparatus of claim 1 wherein the nozzle outlet portincludes a diffuser so that the air stream carrying the entrainedfluoropolymer powder is discharged in a diverging pattern.
 4. Theapparatus of claim 1 wherein the nozzle includes an annular vacuum portadapted to collect fluoropolymer powder not deposited on the threads ofthe fastener.